1. Field of the Invention
The present invention is concerned with a method for powder-metallurgic production of a workpiece from a high-temperature alloy.
2. Description of the Prior Art
In the past, powders in the form of pre-alloys and/or alloy components have been mixed and cold work-hardened and from the mixed and cold work-hardened powders a billet produced by compression. From this product, a workpiece has been formed and subjected to a coarse-grain annealing. Such a method is disclosed, for example, in J. S. Benjamin, Metallurgical Transactions, Vol. I, 1970, p. 2943, and workpieces of particularly high creep strength are obtained thereby. More specifically, the steps involved in the Benjamin process are as follows:
(a) powder mixing; PA1 (b) cold working in an attritor under a protective atmosphere; PA1 (c) canning; PA1 (d) extrusion below the recrystallization temperature; and PA1 (e) coarse grain annealing.
The final product is a rod which cannot be further worked to obtain the form of a forged or cast workpiece otherwise than by grinding.
It is known further (DT-AS 1,923,524) to prepare forged parts from high temperature alloys by first forming a powder - or fusion-metallurgically produced billet in the proportion of at least 4:1 by extrusion pressing. The pressing is done in a temperature range extending from 250.degree. C. below the recrystallization temperature up to the recrystallization temperature. The pressed billet is forged between 760.degree. C. and the recrystallization temperature and then is subjected to a solution treatment above the recrystallization temperature, which is equivalent to a coarse-grain annealing. This method is costly since the billet is first produced from a melt or by sinter metallurgy and this billet must be worked by special processing before being forged.